1. Field of the Invention
The present invention pertains to a system and method of treating ventilatory instability using a ventilatory therapy, a gas modulation therapy, or a combination thereof, and, in particular, to a system and method for treating ventilatory control instability, such as Cheyne Stokes Respiration (CSR), mixed (obstructive and central) apneas, CPAP emergent apneas, complex sleep disordered breathing (CSDB), drug induced central apneas, and high-altitude central apneas, in a dynamic, adaptive fashion.
2. Description of the Related Art
Cheyne-Stokes Respiration (CSR) is one example of ventilatory instability. It is defined as a cyclic alternating pattern of hyperventilation (increased ventilatory drive) and hypoventilation (decreased ventilatory drive). Such recurring cyclic respiratory instability patterns are predominantly experienced by patients suffering from heart failure. The cyclic changes in ventilation in these patients are caused by the instability of the ventilatory control system. This instability is believed to be caused by a high loop gain of the ventilatory feedback control system, an increased chemosensitivity, and longer circulatory delay in the chemoreceptor response.
The instability of the ventilatory control is also experienced in non-heart failure patients with mixed apneas and CPAP emergent central sleep apneas. Mixed apnea is the combination of both central apneas and obstructive apneas. The term apnea, or apneic events, for the purposes of this document includes hypopneas. CPAP emergent central sleep apnea occurs when an upper airway obstruction is eliminated with PAP therapy, unmasking central sleep apneas. These conditions have been treated conventionally using a positive airway pressure (PAP) therapy, such as continuous positive airway pressure (CPAP) therapy. In such cases, the use of PAP therapy leads to cyclic patterns of increased and decreased ventilatory drive and central apneas during the night that cannot be treated with an increase in the CPAP pressure.
One of the treatment options for treating CSR includes using a PAP based servo-ventilation device that delivers a high pressure during inhalation and a lower pressure during exhalation to ventilate or help ventilate the patient. This type of therapy focuses on the periods where the patient experiences reduced ventilation to try to offset this ventilatory decrease. An apparatus for the treatment of CSR is also disclosed in the U.S. patent application Ser. No. 11/235,520 (publication no. US 2006 0070624 A1) (“the '520 application”), the contents of which is hereby incorporated by reference in its entirety. A ventilatory assistance method for treatment is further disclosed in the U.S. Pat. No. 7,077,132 (“the '132 patent”), the contents of which is hereby incorporated by reference in its entirety.
One possible therapy for treating CSR is to attempt to control the carbon dioxide (CO2) gas that the patient receives. This can be done in a variety of ways, such as by providing additional dead space in the patient breathing circuit to cause carbon dioxide (CO2) rebreathing. CO2 can also be provided to the patient by adding CO2 gas from an external supply to the patient breathing circuit. These types of gas modulation therapies in which the CO2 levels received by the patient are regulated, stabilize the patient's ventilatory control system by decreasing the loop gain of that control system.
An increased level of CO2 in the patient's breathing circuit can also be achieved by allowing CO2 rebreathing through the manipulation the leak of exhaled air through an exhalation port on the patient interface. An apparatus for reducing central sleep apnea using these gas is disclosed in the U.S. Pat. No. 7,073,501 (“the '501 patent”), the content of which is hereby incorporated by reference in its entirety.